Equipment under test (EUT) may contribute to ambient noise picked up by the measuring receiver used for electromagnetic interference (EMI) tests. For example, EUTs containing switching power supplies which generate fast rise time pulses often produce broadband emissions.
Prior EMI measurement systems cannot discriminate between narrowband signals and broadband or impulsive noise. Specifically, as a measuring receiver in the form of a spectrum analyzer is swept across a frequency range to measure signals, signals appear at various spectral locations in the frequency spectrum. However, due to complexities in the EUT emissions, the frequency of the signal transmission can vary. Also, the spectrum analyzer can produce measurement errors.
Known methods of determining narrowband signals from broadband signals employ "template matching." Template matching is generally employed in pattern recognition systems, such as those exemplified in U.S. Pat. No. 4,802,231, Davis. The template matching and pattern recognition systems disclosed in Davis attempt to reduce error by creating independent error templates corresponding to patterns which tend to be erroneously matched and linked error templates which are linked to specified reference templates stored for comparison. Upon comparing an unknown pattern with the reference templates, independent error templates, and the linked error templates, the unknown pattern may be identified as a match whenever its test template is most closely matched to a reference template.
Additional methods of pattern recognition and pattern detection using template matching methods are disclosed in U.S. Pat. No. 4,797,941, Lloyd et al. The Lloyd et al. reference discloses comparing an input word to a word stored in template storage means such that if all the inputs are "one," the pattern features defined by a signal distribution correspond to a template word and detection of the pattern is accomplished. The procedure is repeated along an indexed address register to extract a succession of template words until detection is achieved.
Neither the Lloyd et al. nor the Davis patent describes methods, apparatus, or systems which solve a long-felt need in the art for fast and efficient pattern recognition. The Lloyd et al. and the Davis patents also do not provide methods, systems, or apparatus for reducing the time it takes an operator to distinguish narrowband continuous wave signals from broadband emissions or impulsive noise in an EMI test measurement system. This need exists in the art and has not been fulfilled by any of the methods, apparatus, or systems heretofore described.